One type of fluid ejection device is an ink jet printer. The art of ink jet printing is relatively well developed. Commercial products such as computer printers, graphics plotters, and facsimile machines have been implemented with ink jet technology for producing printed media.
Generally, an ink jet image is formed pursuant to precise placement on a print medium of ink drops emitted by an ink drop generating device known as an ink jet printhead. Typically, an ink jet printhead is supported on a movable print carriage that traverses over the surface of the print medium and is controlled to eject drops of ink at appropriate times pursuant to command of a microcomputer or other controller, wherein the timing of the application of the ink drops is intended to correspond to a pattern of pixels of the image being printed.
One embodiment of a Hewlett-Packard ink jet printhead includes an array of precisely formed nozzles in an orifice plate that is attached to an ink barrier layer which in turn is attached to a thin film substructure that implements ink firing heater resistors and apparatus for enabling the resistors. The ink barrier layer defines ink channels including ink chambers disposed over associated ink firing resistors, and the nozzles in the orifice plate are aligned with associated ink chambers. Ink drop generator regions are formed by the ink chambers and portions of the thin film substructure and the orifice plate that are adjacent the ink chambers.
The thin film substructure is typically comprised of a substrate such as silicon on which are formed various thin film layers that form thin film ink firing resistors, apparatus for enabling the resistors, and also interconnections to bonding pads that are provided for external electrical connections to the printhead. The ink barrier layer is typically a polymer material that is laminated as a dry film to the thin film substructure, and is designed to be photodefinable and both UV and thermally curable. In an ink jet printhead of a slot feed design, ink is fed from one or more ink reservoirs to the various ink chambers through one or more ink feed slots formed in the substrate. Examples of ink jet printheads are set forth in commonly assigned U.S. Pat. Nos. 4,719,477 and 5,317,346. In another embodiment, the barrier layer and orifice plate are integral.
During and after the manufacture of ink jet printheads, it is desirable to develop and store data associated with the printhead. Such data can include the wafer lot, wafer number, color, and other information. This data can be stored using an off chip or off die EEPROM. Alternately, the data can be stored on the die itself.
In the past, storing data on the die itself has involved the use of separate fusible links or fuses. The fuses have typically been fabricated as TaAl resistors. One of the issues associated with using on-die fuses stems from the fact that in order to program the fuse, it is electrically blown to define an open circuit. Blowing a fuse on the die, however, can do a significant amount of thermal damage to the surrounding thin film structure. Specifically, blowing an on-die fuse entails breaking overlying passivation layers, melting structure underneath the layers, and the like. Normally, this would not be an issue for substrates that are used in a hermetically-sealed, dry environment. With the ink jet product, however, due to the nature of the fluidic environment in which it operates, even in view of the various barrier materials that can be used to isolate the fuses, there still is a very real possibility for failure to occur due to ink leaking into the fuse area. This is an undesirable situation because not only can stored data be lost, but there is a chance that the overall functionality of the die itself can be compromised.